With the recent outbreak of Equine Herpesvirus, we know you have many questions. The following link to USDA will give you valuable information and should answer most of your questions.
Equine Herpesvirus (EHV) Myeloencephalopathy (USDA)
Following is a link with information from the Texas Animal Health Commission:
Equine Herpesvirus Awareness (Texas Animal Health Commission)